This invention relates to wind wheels or turbines and more particularly to apparatus for providing support and control of furlable soft airfoils used in wind turbines for power generation.
A wind turbine for extracting energy from the wind of the type which utilize soft airfoils (sails) requires some means be provided to extend and retract the airfoil or sail, as well as to control its position with respect to the wind. The usual sailboat arrangement is a boom retained at one end to a mast loaded in tension and compression when the sail is unfurled. The sail is traditionally stored on the boom when partly or fully furled, and the boom is controlled by a sheet reeved through pulleys secured to a deck and may be further supported by a vang secured to the deck. That sailboat system is not particularly adaptable to rotating wind turbines, principally because of the problem of furling and unfurling the sail from a plurality of booms spaced around the turbine. These booms in the wind turbine situation, would be in rotational motion and would require individual means to rotate each boom. This would create a prohibitively massive wind turbine structure. Further, there is no deck to which to secure the sheave (pulley) through which to pass a sheet for control of the boom angle with respect to the wind, or to prevent the boom from lifting under wind stress and spilling air out of the airfoil.
Prior attempts to provide a suitable rigging for soft airfoils in a wind wheel or turbine are shown in the U.S. Patents issued to McIlvaine, No. 242,211; Winge, No. 476,716; Lowe, No. 708,375; Bruneau, No. 704,507; Halladay, No. 138,648; Donnelly, No. 835,667; Wilson, No. 16,818 and German Pat. No. 2,642,570 of Schnitzer.
The patents to McIlvaine, Wilson, Halladay, Donnelly, and Lowe disclose airfoil apparatus for windmills or wheels that involve substantial bracing arrangements in relationship to the amount of airfoil exposed to the wind. The patent to Bruneau shows a mast and sail arrangement having a single support boom for multiple airfoils.
The patent to Winge illustrates a "paddle boat" type of airfoil arrangement in which the airfoils rotate in a plane parallel to the wind direction. Rectangular airfoils are supported by masts with only a spar instead of a boom. The airfoils are designed to be raised and lowered by means of an attached rope.
The German patent to Schnitzer discloses a furlable airfoil mounted on a wheel, but the wheel employs a plurality of heavy, non-compressible, radial mast members. Thus requiring substantial structure to support a small airfoil area. FIG. 9 of Schnitzer illustrates an arrangement of a boom connected to a mast member which is spaced from the spindle. It appears that when the boom is carrying a full sail, the degree to which the boom may pivot about the mast member is limited as the boom length is greater than that of the sail. If not constrained by other means, the boom will stretch and possibly rip the unfurled sail as it swings through a full arc. Much of the wind energy is expended in rotating the massive structures supporting the airfoils, and, accordingly, they do not provide an optimum means to extract energy from the wind. Their use is limited to providing supplemental energy or to single tasks such as pumping water from a well in the ground. Further, because of their mass and low sail/weight ratios, such prior devices require a relatively high threshold wind velocity for start-up and continuing operation. Because of their structural complexity, these prior devices appear unable to withstand a substantial gust of wind without collapsing or sail bursting/shredding.
My copending application entitled "Wind Turbine and Method of Power Generation" filed Mar. 3, 1980, Ser. No. 125,934, now U.S. Pat. No. 4,350,895 issued Sept. 21, 1982, the disclosure of which is incorporated by reference herein, provides a device and method which allows a substantial amount of the energy in the wind to be effectively utilized. It also is able to be used in a range of different wind speeds from light to heavy.
The improved soft airfoil system of this invention may be used in place of the rigging frames, tracks and travelers disclosed in my copending application, with a "V"-shaped boom and spindle mechanism which is lighter, simpler, less costly and permits better and more precise control of the airfoil position and area with respect to wind direction and strength, thus improving the efficiency of the wind turbine expressed in terms of unit airfoil area/unit weight.